AD7707| Datasheet

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3 V/5 V, 10 V Input Range, 1 mW 3-Channel 16-Bit, Sigma-Delta ADC AD7707
FUNCTIONAL BLOCK DIAGRAM
DVDD AVDD REF IN( ) REF IN(+)

FEATURES Charge Balancing ADC 16 Bits No Missing Codes 0.003% Nonlinearity High Level ( 10 V) and Low Level ( 10 mV) Input Channels True Bipolar 100 mV Capability on Low Level Input Channels Without Requiring Charge Pumps Programmable Gain Front End Gains from 1 to 128 Three-Wire Serial Interface SPITM, QSPITM, MICROWIRETM and DSP Compatible Schmitt Trigger Input on SCLK Ability to Buffer the Analog Input 2.7 V to 3.3 V or 4.75 V to 5.25 V Operation Power Dissipation 1 mW max @ 3 V Standby Current 8 A max 20-Lead SOIC and TSSOP Packages GENERAL DESCRIPTION

AD7707
AIN1 AIN2 LOCOM 30k AIN3 VBIAS 5k 5k 15k HICOM MCLK IN MCLK OUT 30k CLOCK GENERATION SERIAL INTERFACE REGISTER BANK SCLK CS DIN DOUT A = 1 128 MUX BUF PGA CHARGE BALANCING A/D CONVERTER MODULATOR DIGITAL FILTER

AGND

DGND

DRDY

RESET

The AD7707 is a complete analog front end for low frequency measurement applications. This three-channel device can accept either low level input signals directly from a transducer or high level ( 10 V) signals and produce a serial digital output. It employs a sigma-delta conversion technique to realize up to 16 bits of no missing codes performance. The selected input signal is applied to a proprietary programmable gain front end based around an analog modulator. The modulator output is processed by an on-chip digital filter. The first notch of this digital filter can be programmed via an on-chip control register allowing adjustment of the filter cutoff and output update rate. The AD7707 operates from a single 2.7 V to 3.3 V or 4.75 V to 5.25 V supply. The AD7707 features two low level pseudodifferential analog input channels, one high level input channel and a differential reference input. Input signal ranges of 0 mV to +20 mV through 0 V to +2.5 V can be accommodated on both low level input channels when
operating with a VDD of 5 V and a reference of 2.5 V. They can also handle bipolar input signal ranges of 20 mV through 2.5 V, which are referenced to the LCOM input. The AD7707, with a 3 V supply and a 1.225 V reference, can handle unipolar input signal ranges of 0 mV to +10 mV through 0 V to +1.225 V. Its bipolar input signal ranges are 10 mV through 1.225 V. The high level input channel can accept input signal ranges of 10 V, 5 V, 0 V to +10 V and 0 V to +5 V. The AD7707 thus performs all signal conditioning and conversion for a threechannel system.
SPI and QSPI are trademarks of Motorola, Inc. MICROWIRE is a trademark of National Semiconductor Corporation.

The AD7707 is ideal for use in smart, microcontroller or DSPbased systems. It features a serial interface that can be configured for three-wire operation. Gain settings, signal polarity and update rate selection can be configured in software using the input serial port. The part contains self-calibration and system calibration options to eliminate gain and offset errors on the part itself or in the system. CMOS construction ensures very low power dissipation, and the power-down mode reduces the standby power consumption to 20 uW typ. These parts are available in a 20-lead wide body (0.3 inch) small outline (SOIC) package and a low profile 20-lead TSSOP.
PRODUCT HIGHLIGHTS

1. The AD7707 consumes less than 1 mW at 3 V supplies and 1 MHz master clock, making it ideal for use in low power systems. Standby current is less than 8 uA. 2. On-chip thin-film resistors allow 10 V, 5 V, 0 V to +10 V and 0 V to +5 V high level input signals to be directly accommodated on the analog inputs without requiring split supplies or charge-pumps. 3. The low level input channels allow the AD7707 to accept input signals directly from a strain gage or transducer removing a considerable amount of signal conditioning. 4. The part features excellent static performance specifications with 16 bits, no missing codes, 0.003% accuracy and low rms noise. Endpoint errors and the effects of temperature drift are eliminated by on-chip calibration options, which remove zero-scale and full-scale errors.

REV. A
Information furnished by Analog Devices is believed to be accurate and reliable. However, no responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other rights of third parties which may result from its use. No license is granted by implication or otherwise under any patent or patent rights of Analog Devices. One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A. Tel: 781/329-4700 World Wide Web Site: http://www.analog.com Fax: 781/326-8703 Analog Devices, Inc., 2000